STM/STS and ARPES Studies of In-Situ Strain Control of van der Waals Materials

Mechanical strain has emerged as an important tool for gaining insight into, and tuning the behavior of, quantum materials. This is particularly true for 2D materials and moiré structures, where the measured correlated electronic states have been shown to be exceptionally sensitive to lattice strain. Previous in situ strain measurements have relied on methods such as piezo-based stacks, thermal expansion mismatch, and nanoscale bubbles. However, tunable strain measurements have focused on the linear, low-strain regime. Here, we perform scanning tunneling microscopy/spectroscopy (STM/STS) and micron-spot size angle-resolved photoemission spectroscopy (micro-ARPES) measurements on a variety of van der Waals systems under in-situ tunable tensile strain in the large-strain regime. Our atomic-scale measurements on graphene show that it can be severely deformed before the onset of failure while experiments on transition metal dichalcogenides (TMDs) show an increase in atomic-scale defect density as well as shifts in ARPES spectral weight with increasing strain.